1. Field
Example embodiments relate to a method of manufacturing a semiconductor memory device. Other example embodiments relate to a method of surface treating a phase change layer and a method of manufacturing a phase change memory device.
2. Description of the Related Art
A phase change material is a material that may switch between a crystalline state and an amorphous state with changes in temperature. The crystalline or amorphous state of the phase change material is reversible. For example, the phase change material may be change from the crystalline state to the amorphous state, or from the amorphous state to the crystalline state. The resistance of the phase change material in the crystalline state may be lower than the resistance of the phase change material in the amorphous state. Therefore, there are clearly two different states of resistance in phase change material.
A phase change memory device (may be referred to as a PRAM) may be a memory device using the above-described phase change material as a storage node.
In general, a PRAM may include a transistor and a storage node that is electrically connected to the transistor and may include a phase change material. The PRAM may function as a memory by utilizing the resistance difference between the amorphous and crystalline states of the phase change material. Presently, various types of phase change materials that may be used in PRAMs are known, for example, a GeSbTe (GST) alloy.
Like other memory devices, the PRAM may also reduce its operating current. A current for switching the phase change material from the crystalline state to the amorphous state in a PRAM may be referred to as a reset current, and a current for switching the phase change material from the amorphous state to the crystalline state may be referred to as a set current. The temperature of the phase change material for switching the phase change material in the crystalline state to the amorphous state should be greater than the melting point of the phase change material. Thus, the reset current may be a current for increasing the temperature of the phase change material above the melting point.
In order to switch the phase change material from the amorphous state to the crystalline state, the temperature of the phase change material may be increased above a predetermined or given temperature, but the predetermined or given temperature may be lower than the melting point of the phase change material. Accordingly, the reset current may be higher than the set current. The transistor used in the PRAM may be limited depending on the amount of the reset current. Even to reduce the power consumption and to increase the integration degree of the PRAM, the reset current of the PRAM should be reduced. Also, the reset current should be greater than the set current.
A GeSbTe (GST) layer used widely as a phase change material for PRAMs may be formed using a physical vapor deposition (PVD) method. However, when a GST layer is formed using a PVD method, the growth of the GST layer may be difficult to control, and the deposition speed of the GST layer may be lower. Also, the densification of the GST layer may be decreased. Such problems may be overcome to some degree by forming a GST layer using an atomic layer deposition (ALD) method. However, even when using an ALD method for forming a GST layer, the following problems may occur.
For example, a GST layer may not be formed only on a bottom electrode contact (BEC) but also on a silicon oxide layer around the BEC. An organic metal compound may be used as a source material for a GST layer to form a GST layer. The organic metal compound may have an alkyl radical. Because the organic metal compound may not be easily absorbed on a silicon oxide layer at a relatively low temperature, the thickness of the GST layer may not be constant, and the step coverage of the GST layer may be decreased.